Insulate Pipes OUTSIDE wall and Kerdi around shower valve

I am getting ready to insulate the pipes in my shower. This is on an OUTSIDE wall.

I am going to use the black foam insulation and fiberglass insulation. My suestion is; should I split the fiberglass batting and tuck it in front of and behind the pipe or just stuff it behind the pipe?

Also should the drywall and Kerdi be brought in tight around the shower valve or should I use the plastic rough-in spacer and only bring the drywall and kerdi up to the plastic?

Normally, if you get the Kerdi close enough to the rough-in piece and tile it, the eschution with its seal will complete things enogh so you don't need to bring the Kerdi further in. If you really want to seal that area, get a tube of KerdiFix (or another urethane sealant), and seal it to the valve. I don't recommend that, nor do I feel it is necessary since the trim plate should seal it well enough, and gluing to the valve can be a big pain if you need to do service. Around things like body sprays, depending on their trims and the seals they may have, you may want to seal the Kerdi to the fixture with the sealant.

I would have tried to rearrange things so the pipes could be on an inside wall, but that's too late. You want the pipes in the room side of the cavity to get as much room heat as possible to prevent freezing. See what the concensus is before you jump off the deep end.

This is not new construction. I am replacing the original shower that fell apart because they did not use Kerdi. I have no choice but to put the pipes in the same place they were. All I did was replace the old PB with PEX and put in a new diverter.

We recently remodeled our bath in an old 1920's house. Exterior wall, stucco, cold winters. We used the closed cell expanding foam (not the rapid open cell stuff, it can hold water like a sponge). I think the product is handi-foam and they sell a DIY kit. It is not cheap, but it insulates the dickens out of small spaces.

The water we get out of there is considerably warmer than it used to be.